Process of electroplating metallic cadmium and electrolytic bath therefor



Patented Dec. 1925.

UNITED STATES cmY'roN PATEN'T- OFFICE...

M. HOFF, OF CLEVELAND, OHIO, ASSIGNOR TO THE GB ASSELLI GHEMIIICAL- COMPANY, or CLEVELAND, 01110, A CORPORATION OF OHIO. 1

rnocnss or, nnncrnornn'rme mnranmc camrrum AND ELECTROLYTIC Barn i'-THERI EFOR Ho Drawing.

1 '0 all whom it may concern:

Be it known that I, CLAYTON M. Horr, a citizen of the United States, residing at Cleveland, in the county of Guyahoga and 5 State of Ohio, have invented certain new and useful Improvements in Processes of Electroplating Metallic Cadmium and Electrolytic Bath 'lherefor, of which the follow ing is alspecification.

This invention relates to a process of electroplating metallic cadmium and to a novel electrolytic bath or solution containing cadmium, from Whiclimetallic cadmium may be electroplated in the form of pure, uniform 1| and smooth deposits.

As is known, thin depositsof cadmium upon other metals, for instance iron and steel, such as may he produced by electrodeposition, possess admirable protecting 8 properties, but considerable difliculty has been encountered in devising a sat sfactory method for producing deposits or coa tings of cadmium havingdesired characteristics.

Amongthe difiiculties encountered may be I mentioned the inability to form deposlts of the desired purity, umformity and smoothness. By the employmentof my invention.

these difliculties are overcome and in addition I am able to deposit cadmium rapidly so and quantitatively, if desired, from solu- -tions thereof prepared in accordance with the invention, even when such solutions' contain'also zinc. As will be-apparent, the invention m ay be putto uses other than for 85 the electrodepositlon of cadmium in the form of protective or ornamental coatings upon 'metals. For instance, the. invention may be applied for the. quantitative determination of cadmium or for the quantitative deter- 40 mination of zinc in the presence of cad-.

mium or for the quantitative determination of both cadmium and zinc in admixtures thereof. A noteworthy feature of the in.- vention is that it provides a process where by the commercial supplies of c dmium available for plating purposes, both in the.

form of the metal and in the form of compounds of cadmium which usually contain zinc or zinc compounds, may, be used directly 60 and :without preliminary purification-for'the removal of zinc. p I

' The electroplating solution of my inven- Application filed January 17, 1924. Serial No. 686,898.

tion may be prepared by dissolving cadmium oxid or. hydroxid or a salt of cadmium such as the sulfate, either pure or contaminated or mixed with zinc oxid 0r hydroxid or a. salt such as the sulfate, in an a ueous solution of ammonia and'adding to t e resplting-solution a cyanide. Solutions so prepared possess theproperty of permitting the electrodeposition of pure cadmium rapidly and completely, if desired, in the form of smooth homogeneous deposits, presumably due to thenature of the chemical combination of the cadmium or the cadmium and zinc in the soluble compounds thereof present in the solutions.

. An application of the invention for the quantitative determination of cadmium and zinc is illustrated in the following example,

it being understood of course that the invention is not limited to the specific details recited therein, excepting in sQ-far as such details are embodied in the appended claims.

A mixture of cadmium sulfate and'zinc sulfate containing sayequal parts byweight of the two-metals is dissolved in a quantity of water only suflicient to give a'strong solu-' tion, say about one-half saturated at room temperature and the resulting aqueous solution is treated with a strongaqueous solution of ammonium hydroxid until the hydroxids of zinc and cadmium first formed redissolve. vTo each-'5 cubic centimeters of the resulting ammoniacal solution are added about 10 cubic centimeters of a 14% ammonium hydroxid solution and about 7.5 grams of sodium cyanid and the resulting solution is diluted with water to about'four times the volume of the ammoniacal solution carrying the cadmium deposit, is removed from the electrolyte \while washing, with water and without breaking the current flow, washed with alcohol, dried at 100 C. and weighed.

For the determination of the zinc content of the residualsolution about 20 grams-of caustic soda are added for each 20 cc. of solution and its ammonia content removed by boiling. The. resulting solution is then cooled and electrolyzed at room temperature, usinga voltage across the electrodes of t to 5 volts and a current density of about 2 amperes per" 100 square centimeters of electrode surface, the distance between the electrodes being about 15 centimeters. About two hours are sufficient to complete the deposition of the zinc. lhe zinc maybe deposited directly upon the cadmium coated electrode and the deposit washed,- dried "and it weight determined in the same way as the cadmium coating.

The following table illustrates the accuracy of the process for the quantitative determination of cadmium and zinc in mixtures thereof.-

' Weight taken Weight found Test Cadmium Zinc Cadmium Zinc 4000 0000 3988 0000 4000 0000 3990 .0000 4000 0100 3985 0110 3000 0500 3008 0483 4000 4000 4002 Not deter mined The application of the invention for commercial electroplating is apparent from the foregoing example, it being understood of course that in electroplating cadmium as a protective coating upon metals the depositlon of the cadmium content of the electrolytefneed not be carried tocompletion; but

the electrodeposition maybe carried to any suitable point and the electrolyte then renewed by the addition to it of the neees sary ingredients or the renewing ingredients may be added during the electrolysis until the zinc content of the electrolyte reachesstood that raw materials other than cad- 'mium and zinc oxids; hydroxids and sulfates may be used as starting materials, for in stance Q other salts of zinc and cadmium,

although this connection it is noted that the salt formin groupof some salts may interfere with t e-operation of the process. The sulfates are. erhaps"'the cheapest salts of the metals an are'readil formed from other salts or compounds or rom. the metals themselves and therefore constitute -a very the concentration of the electrelyte, proportions 'of the reagents, the temperature: of operation, voltages and current densities may be made by one skilled in the artto which .this' invention relates without. departure fromthe spirit of the invention. It is further noted that the use of suitable addition agents designed to. produce smoother and more uniform deposits, such as inorganic salts and organic materials of which a large number are known, is not to be regarded as a departure from the invention.

Electro-deposits of cadmium free of zinc, such as those produced in accordance with my invention, have been found to be very resistant as compared with deposits containing zinc, as hasbeen demonstrated by the salt spray test.

I claim: r 1. Process of electrodeposltmg cadmium which comprises preparing an alkaline s0-.

lution containing a compound of cadmium, a compound of ammonlaand a cyanide and electrolyzing said solution.

2. Process of electrodepositing cadmium satisfactory starting material.- Variations in which comprises'preparing-an ammoniacal solution of a compound of cadmium containing cyanide and electrolyzing said solution.

3. Process of electrodepositing cadmium which comprises dissolving acompound of cadmium in an aqueous solution of ammonia,

dissolving an alkali metal cyanide in the resulting, solution and electrolysis.

4. Proeesss of electrodepositing cadmium which comprises electrolyzing an aqueous solution containing the reaction products of ammonia water, a compound ofcadmium,

and' an alkali metal cyanide.

subjecting the same to 5. Process of electrode 'o'siting cadmium from a solution thereo containing zinc which .comprises preparing an ammoniacal solutionof cadmium and zmccontainingla-n alkali metal cyanide and electrolyzing said solution.

6. Process of separating cadmium and zincom mixtures containin monia, adding a cyanide to the solution, electrolyzing the solution until the, deposition of to the residual solution and neating the same until the ammonia content thereof is expelled therefrom, and subjecting the resulting solution to electrolysis,-

the same orthe1r compounds which compr ses dlssolvmg -.sa1d materlals in an aqueous solution of amcadmium is complete, adding caustic soda an alka sub]0ting the resulting solution to elec- .7. Processof electrodepositing cadmium which comprises preparing a mixture of cadmium sulfate and zinc sulfate from a raw materialcontainingcadmium and zinc or their compounds, dissolving the mixture in an aq1 eons-solution of ammonia, adding metal cyanide to the solutionand trolysis. I w

8. As an electrolyte for the electrode'posi-' tion of cadmium, an aqueoua solution of a' compound of cadmium, ammonia, and alkali metal cyanide-and their reaction products.

9; Anelectrolyte for the clectrodepo'sition of cadmium comprising the reaction prodnets of cadmium sulfate, aqua ammonia, and sodium cyanide.

10. As an electrolyte for the electrodepo sition' of cadmium, an ammoniacal aqueous solution containing cadmium, zinc and a soluble cyanide.

11. An electrolyte for the electrodeposisignature. CLAYTON 12 HOFF. 

